Absorption of CO2 and CO gases and furfural in insulating oil into paper insulation in oil-immersed transformers

This paper relates to diagnostic methods for oil-immersed transformers. Diagnosis of internal condition of oil-immersed transformers using dissolved gas analysis technique is widely performed to monitor abnormalities in transformers or to estimate life expectancy of transformers. Carbon dioxide and carbon monoxide gases have been found to be good indicators of transformer condition. Furfural has drawn attention of experts as another good indicator since a few years ago. It is commonly observed that concentration of CO₂ and CO gases in insulating oil in transformers fluctuates appreciably depending on time of sampling. The authors examine the possible causes of the fluctuation and come to the conclusion that temperature dependence of absorption of those gases into paper insulation in transformers is the main cause of the fluctuation. This paper describes theoretical and experimental studies of the phenomenon in detail. It is shown that the accuracy of dissolved gas analysis can be greatly improved if the phenomenon is taken into account